Substantial underreporting is typical in interviewing respondents on their drug use and other sensitive behaviors. Self-administered questionnaires and indirect questioning techniques have been shown to increase respondents' willingness to report stigmatizing behavior. However, these techniques require that the respondents be able to read, and to understand branching or contingent questions. Computer-assisted self-interviewing (CASI) and audio-CASI systems do not require literacy on the part of the respondent and avoid the difficulties of implementing complex instructions. These systems provide the same privacy enhancements of traditional self-administered questionnaires. In addition, audio-CASI allows researchers to ask questions in any language of any respondent who can see and hear, and is suitable for use in a variety of settings. Tables, notes, references